The invention relates to a valve control of an internal combustion engine having a camshaft and a cam sleeve which is displaceably arranged on the camshaft, on which the cams for the valve displacement are formed.
In particular, the valve control serves for the exhaust valve deactivation as a part of the control for the cylinder deactivation in internal combustion engines for lowering the fuel consumption. By deactivating the inlet and exhaust valves combined with an interruption of the fuel supply half of the cylinders are deactivated and thus the operating point of the engine, because of the mean pressure increase, is displaced into a range of better efficiency.
In addition to mechanical solutions with more than one crankshaft, solutions for the cylinder deactivation are also known from the prior art, for example in which rotation the fuel injection and mixture ignition are enabled or shut-off in a controlled manner.
In addition, a cam sleeve that can be displaced on the camshaft via an actuator is already known from the prior art. However, because of the different control times of individual cylinders and the displacement of the cams on the camshaft in circumferential direction, a separate actuator and a separate cam sleeve have had to be employed for each cylinder up to now. In terms of control, this is complicated, susceptible to error and expensive because of the high number of components.
Building on what is known, the invention is based on the object of providing a valve control for an exhaust valve deactivation with which the valves of a plurality of cylinders can be simultaneously controlled and thus the associated cylinders can be activated or deactivated.
This and other objects are achieved according to the invention by a valve control of an internal combustion engine having a camshaft and a cam sleeve which surrounds the camshaft and is fastened in an axially displaceable manner. The cam sleeve has cams associated with individual valves and extending in the radial direction, wherein the cam sleeve during rotation is displaceable relative to the camshaft in the axial direction by an actuator. The cam sleeve comprises at least two axial sections, which are displaceable relative to one another in the axial direction via the actuator engaging in the axial sections.
The cam sleeve is provided on the region of the camshaft in which the cylinders are to be deactivated. In the case of a six-cylinder in-line engine, according to the invention a cam sleeve is arranged on the camshaft for three adjacent cylinders, in order to switch the camshaft to active or inactive via the displaceable cam sleeve for the three cylinders. Since the cams in the region of the camshaft with cam sleeve are not provided on the camshaft itself but on the cam sleeve, an axial displacement of the cam sleeve away from the valves results in that the cams do not act on the valves but, axially spaced therefrom, rotate past the valves. For activating the valve displacement via the cams, the cam sleeve is again displaced into the original position in the axial direction. On the further three cylinders the camshaft comprises its conventional cams so that on these cylinders a valve displacement always takes place and thus only three of the six cylinders can be deactivated.
Compared with the prior art, the invention is characterized in that the cam sleeve is formed in multiple parts and is thus suitable to realize a deactivation of valves on a plurality of cylinders with only one actuator.
In one embodiment, the valve control according to the invention is provided such that the at least two axial sections of the cam sleeve are displaceable relative to one another in the axial direction during the engagement of the actuator by rotation of the cam sleeve. Because of the fastening of the cam sleeve on the camshaft, the camshaft and cam sleeve rotate coaxially with one another. The two axial sections make it possible during the rotation of the camshaft with cam sleeve to initially move a cam sleeve section of a first cylinder axially and thus deactivate the valve displacement of this cylinder. At that time, the cams of the cam sleeve still act on the associated valves on the adjacent cylinders so that a displacement of the cam sleeve in the region of these cylinders is still impossible. The continuing rotation brings the cams of the cam sleeve on the further cylinders into a position that is disengaged from the valves so that, subsequently, an axial displacement of the second axial section of the cam sleeve is possible.
The valve control is therefore characterized in that during the rotation of the cam sleeve over a predetermined angle, in particular 180°, by the actuator, the first axial section is initially displaced in an axial direction and upon a continuation of the rotation over a further predetermined angle, in particular further 180°, the second axial section is subsequently displaced in the same axial direction until the first and second axial sections of the cam sleeve at the cylinders to be deactivated, axially displaced, again lie against one another. When both axial sections, following a 360° rotation of the camshaft, have been axially displaced, the cams of the cam sleeve no longer act on the valves and the cylinders are deactivated.
To achieve the axial displacement of the axial sections of the cam sleeve, it is provided, in an embodiment, that in an outer circumferential surface of the two axial sections of the cam sleeve at least two sliding grooves extending in the circumferential direction and the axial direction run in each case, in which the actuator engages. The sliding grooves of the axial sections merge into one another at a transitional position of the axial sections. The transitional position is determined by the axial relative position of the axial sections on the camshaft relative to one another.
An embodiment, in which the actuator comprises at least one first actuator pin, which engages in the first sliding groove of the axial sections of the cam sleeve and consecutively displaces the axial sections in a first axial direction upon the rotation of the cam sleeve described above, is advantageous. In addition, an embodiment is advantageous in which the actuator comprises at least one second actuator pin, which engages in the second sliding groove of the axial sections of the cam sleeve and consecutively displaces the axial sections in a second axial direction upon a counter-rotation of the cam sleeve. With such an embodiment, the actuator engages with, in each case, one actuator pin in a respective sliding groove. The engagement in the first sliding groove serves for an axial displacement in a first direction and the engagement in the second sliding groove serves for a resetting into the original axial position.
On the actuator, the actuator pins are arranged fixed in position so that the axial sections are displaced in the axial direction relative to the actuator while the actuator pins during the rotation of the cam sleeve slide in the sliding grooves. The actuator itself is likewise fixed in position.
In a development of the invention, it is further provided that the sliding grooves have a tapering cross section with oblique radial contact surfaces, against which the actuator pins lie in a flat manner. Here, the radial contact surfaces mainly extend at the same angle as the actuator pins so that they engage in the sliding grooves without play. Because of this, load peaks during the switching process, and thus wear on the actuator pins and sliding grooves, are avoided.
In another embodiment of the invention, the camshaft has an axial end stop which delimits the axial moveability of the at least two axial sections. In an advantageous exemplary embodiment, the axial end stop is formed by retaining devices, for example locking balls, arranged between the camshaft and the at least two axial sections and preloaded in the radial direction. The retaining devices in each case releasably engage in inner grooves provided on radial inner surfaces of the at least two axial sections. Because of this, sliding of the cam sleeve off the camshaft is prevented. In addition, fastening of the cam sleeve on the camshaft is preferentially effected via splines.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.
The same reference characters denote the same parts in all views.